The present invention relates to a plastic lens composition, a plastic lens obtained by curing the composition, and a process for producing the plastic lens.
More specifically, the present invention relates to a plastic lens composition having a refractive index of 1.58 or more at 25xc2x0 C. and a specific gravity of 1.40 or less at 23xc2x0 C.; a lightweight plastic lens having a high refractive index, obtained by curing the composition; and a process for producing the plastic lens.
Organic glass is lightweight, compared with inorganic glass, and, therefore, organic glasses comprising a polymer such as diethylene glycol bis(allyl carbonate) represented by CR-39 (trade name, produced by PPG) or methyl methacrylate have heretofore been used. However, these organic glasses are disadvantageous in that the refractive index which is from 1.49 to 1.50 is relatively low as compared with inorganic glass (refractive index of white crown glass: 1.523), the thickness is larger than the inorganic glass to impair the effect of reducing the weight and when used as a lens for visual acuity correction, a higher degree of myopia incurs a poor appearance.
In order to cope with this, various organic glasses using a diallyl phthalate-based monomer have been proposed. However, these are fragile or have a problem in transmittance. When this monomer is diluted with a monofunctional polymerizable monomer to deal with these problems, the resistance against heat or solvent is impaired and the capability, as an organic glass, is insufficient.
An allyl ester having an allyl ester group at a terminal, and having inside thereof the following structure derived from a polyhydric saturated carboxylic acid and a polyhydric saturated alcohol, is also known:
CH2xe2x95x90CHCH2O{CORCOOBxe2x80x2O}nCORCOOCH2CHxe2x95x90CH2
wherein R represents a divalent organic residue having from 1 to 20 carbon atoms, Bxe2x80x2 represents a divalent organic residue derived from a diol, and n represents a number of 1 to 20.
This allyl ester provides a cured material having very excellent impact resistance, but, because an aliphatic hydrocarbon Bxe2x80x2 is used inside, even if terephthalic acid or isophthalic acid is used as the polyvalent saturated carboxylic acid, the refractive index is lower than that of a cured material of diallyl terephthalate monomer or diallyl isophthalate monomer.
In Japanese Unexamined Patent Publication No. 3-124715 (JP-A-3-124715), the present inventors have proposed an allyl ester resin containing a halogen. However, this resin, as it is, has a high viscosity and a very large specific gravity and cannot be used as an optical material.
In Japanese Unexamined Patent Publication No. 7-33831 (JP-A-7-33831), the present inventors have also proposed a composition containing an allyl ester resin having incorporated thereinto bromine and an optical organic glass obtained by curing the composition. However, in view of the comfort while wearing eyeglasses, an optical organic glass having a low specific gravity and a high refractive index is required. Furthermore, in order to increase the productivity, a composition for plastic articles is required to show good filterability in the filtering of the plastic article composition to ensure easy flowing and quick filling into a mold. To satisfy these requirements, the plastic article composition is required to have a lower viscosity.
On taking account of the balance among three factors of viscosity, the refractive index of the cured material and the specific gravity of the cured material, the composition described in JP-A-7-33831 does not match recent requirements of the market and the composition of JP-A-7-33831 is not an optimal proposal for the recent requirements of the market.
In order to meet with the requirements of the market, an object of the present invention is to solve the above-described problems and provide a plastic lens composition having a viscosity sufficiently low to enable the use for plastic lens materials or other optical materials and ensuring a high refractive index and a relatively low specific gravity of the cured material. Other objects of the present invention are to provide a plastic lens obtained by curing the composition and to provide a process for producing the plastic lens.
As a result of extensive investigations to overcome the above-described problems, the present inventors have found that when a (meth)allyl ester-based compound containing bromine is used, a plastic lens composition capable of providing a cured material favored with a high Abbe number and a relatively small cure shrinkage can be obtained. The present invention has been accomplished based on this finding.
More specifically, the present invention (I) relates to a plastic lens composition comprising a component (xcex1) shown below as an essential component, wherein a cured material obtained by curing the composition has a refractive index of 1.58 or more at 25xc2x0 C. and a specific gravity of 1.40 or less at 23xc2x0 C.:
Component (xcex1)
a compound having at least one group represented by the following formula (1) as a terminal group and a group represented by the following formula (2) as a repeating unit: 
wherein each R1 independently represents an allyl group or a methallyl group and each A1 independently represents an organic residue derived from a dicarboxylic acid or a carboxylic anhydride; 
wherein each A2 independently represents an organic residue derived from a dicarboxylic acid or a carboxylic anhydride and each X is independently an organic residue and the X""s represent one or more organic residues containing, as an essential component, an organic residue derived from a bromine-containing compound having two or more hydroxyl groups, provided that by the ester bonding, X can have a branched structure having a group of formula (1) as a terminal group and a group of formula (2) as a repeating unit.
The present invention (II) relates to a plastic lens composition comprising a component (xcex1) and a component (xcex2) shown below, wherein a cured material obtained by curing the composition has a refractive index of 1.58 or more at 25xc2x0 C. and a specific gravity of 1.40 or less at 23xc2x0 C.:
Component (xcex1)
a compound having at least one group represented by the following formula (1) as a terminal group and a group represented by the following formula (2) as a repeating unit, in an amount of 10 to 60% by mass based on whole curable components: 
wherein each R1 independently represents an allyl group or a methallyl group and each A1 independently represents an organic residue derived from a dicarboxylic acid or a carboxylic anhydride; 
wherein each A2 independently represents an organic residue derived from a dicarboxylic acid or a carboxylic anhydride and each X is independently an organic residue and the X""s represent one or more organic residues containing, as an essential component, an organic residue derived from a bromine-containing compound having two or more hydroxyl groups, provided that by the ester bonding, X can have a branched structure having a group of formula (1) as a terminal group and a group of formula (2) as a repeating unit;
Component (xcex2)
at least one compound selected from the group consisting of compounds represented by the following formulae (3) and (4), in an amount of 10 to 90% by mass based on whole curable components: 
xe2x80x83wherein R2 and R3 each independently represents an allyl group or a methallyl group; 
wherein R4 and R5 each independently represents an allyl group or a methallyl group.
The present invention (III) relates to a plastic lens composition comprising a component (xcex1), a component (xcex2) and a component (xcex3) shown below, wherein a cured material obtained by curing the composition has a refractive index of 1.58 or more at 25xc2x0 C. and a specific gravity of 1.40 or less at 23xc2x0 C.:
Component (xcex1)
a compound having at least one group represented by the following formula (1) as a terminal group and a group represented by the following formula (2) as a repeating unit, in an amount of 10 to 60% by mass based on whole curable components: 
wherein each R1 independently represents an allyl group or a methallyl group and each A1 independently represents an organic residue derived from a dicarboxylic acid or a carboxylic anhydride; 
wherein each A2 independently represents an organic residue derived from a dicarboxylic acid or a carboxylic anhydride and each X is independently an organic residue and the X""s represent one or more organic residues containing, as an essential component, an organic residue derived from a bromine-containing compound having two or more hydroxyl groups, provided that by the ester bonding, X can have a branched structure having a group of formula (1) as a terminal group and a group of formula (2) as a repeating unit;
Component (xcex2)
at least one compound selected from the group consisting of compounds represented by the following formulae (3) and (4), in an amount of 10 to 90% by mass based on whole curable components: 
wherein R2 and R3 each independently represents an allyl group or a methallyl group; 
wherein R4 and R5 each independently represents an allyl group or a methallyl group;
Component (xcex3)
at least one compound selected from the group consisting of dibenzyl maleate, diphenyl maleate, dibenzyl fumarate, diphenyl fumarate, (meth)allyl 2-phenylbenzoate, (meth)allyl 3-phenylbenzoate, (meth)allyl 4-phenylbenzoate, (meth)allyl xcex1-naphthoate, (meth)allyl xcex2-naphthoate, (meth)allyl o-chlorobenzoate, (meth)allyl m-chlorobenzoate, (meth)allyl p-chlorobenzoate, (meth)allyl 2,6-dichlorobenzoate, (meth)allyl 2,4-dichlorobenzoate, (meth)allyl o-bromobenzoate, (meth)allyl m-bromobenzoate and (meth)allyl p-bromobenzoate, in an amount of 0 to 20% by mass based on whole curable components.
The present invention (IV) is the plastic lens composition of the present invention (I), (II) or (III) which further comprises an ultraviolet absorbent and/or a light stabilizer in an amount of 0.01 to 2 parts by mass per 100 parts by mass of whole curable components in the plastic lens composition.
The present invention (V) is the plastic lens composition of the present invention (I), (II), (III) or (IV) which further comprises an antioxidant in an amount of 0.01 to 5 parts by mass per 100 parts by mass of whole curable components in the plastic lens composition.
The present invention (VI) is the plastic lens composition of the present invention (I), (II), (III), (IV) or (V) which further comprises at least one radical polymerization initiator in an amount of 0.1 to 10 parts by mass per 100 parts by mass of whole curable components in the plastic lens composition.
The present invention (VII) is a plastic lens having a refrative index of 1.58 or more at 25xc2x0 C. and a specific gravity of 1.40 or less at 23xc2x0 C., which is obtained by curing the plastic composition of the present invention.
The present invention (VIII) is a plastic lens having a refrative index of 1.58 or more at 25xc2x0 C., a specific gravity of 1.40 or less at 23xc2x0 C., a carbon concentration by elemental analysis of 50.0 to 70.0% by mass and a bromine concentration by elemental analysis of 9.0 to 15.0% by mass.
The present invention (IX) is a process for producing the plastic lens of the present invention.